Chee Yen Leow

On the Study of Analogue Network Coding for Multi-Pair, Bidirectional Relay Channels

We consider a scenario where multiple pairs of users exchange information within pair, with the help of a dedicated multi-antenna relay. The protocol integrates the idea of analogue network coding in mixing two data streams originating from the same user pair, together with the spatial multiplexing of the data streams originating from different user pairs. The key feature of the protocol is that it enables both the relay and the users to participate in interference cancellation. We propose several beamforming schemes for the multi-antenna relay and evaluate the performance using information theoretical metrics such as ergodic capacity, outage probability and diversity and multiplexing tradeoff. Analytical and simulation results justify that the ergodic capacity, outage probability and diversity and multiplexing tradeoff of the proposed beamforming schemes outperform comparable schemes.

A Comprehensive Survey of Pilot Contamination in Massive MIMO—5G System

Massive MIMO has been recognized as a promising technology to meet the demand for higher data capacity for mobile networks in 2020 and beyond. Although promising, each base station needs accurate estimation of the channel state information (CSI), either through feedback or channel reciprocity schemes in order to achieve the benefits of massive MIMO in practice. Time division duplex (TDD) has been suggested as a better mode to acquire timely CSI in massive MIMO systems. The use of non-orthogonal pilot schemes, proposed for channel estimation in multi-cell TDD networks, is considered as a major source of pilot contamination in the literature due to the limitations of coherence time. Given the importance of pilot contamination in massive MIMO systems, we provide an extensive survey on pilot contamination, and identify other possible sources of pilot contamination, which include hardware impairment and non-reciprocal transceivers. We review established theories that have analyzed the effect of pilot contamination on the performance of massive MIMO systems, particularly on achievable rates. Next, we categorize the different proposed mitigation techniques for pilot contamination using the following taxonomy: pilot-based approach and subspace-based approach. Finally, we highlight the open issues, such as training overhead, deployment scenario, computational complexity, use of channel reciprocity, and conclude with broader perspective and a look at future trends in pilot contamination in massive MIMO systems.

PSOGSA-Explore

Graphical abstractDisplay Omitted HighlightsWe propose a new algorithm to lower the sidelobes in collaborative beamforming.We achieved up to 100% improvement in sidelobe reduction.Variable parameter tuning is simplified in the proposed algorithm.The proposed algorithm successfully avoids the problem of premature convergence.The proposed method does not increase the computational complexity of the system. A conventional collaborative beamforming (CB) system suffers from high sidelobes due to the random positioning of the nodes. This paper introduces a hybrid metaheuristic optimization algorithm called the Particle Swarm Optimization and Gravitational Search Algorithm-Explore (PSOGSA-E) to suppress the peak sidelobe level (PSL) in CB, by the means of finding the best weight for each node. The proposed algorithm combines the local search ability of the gravitational search algorithm (GSA) with the social thinking skills of the legacy particle swarm optimization (PSO) and allows exploration to avoid premature convergence. The proposed algorithm also simplifies the cost of variable parameter tuning compared to the legacy optimization algorithms. Simulations show that the proposed PSOGSA-E outperforms the conventional, the legacy PSO, GSA and PSOGSA optimized collaborative beamformer by obtaining better results faster, producing up to 100% improvement in PSL reduction when the disk size is small.

Joint Beamforming and Power Management for Nonregenerative MIMO Two-Way Relaying Channels

We consider multiple-input-multiple-output (MIMO) two-way relaying channels where a pair of multiantenna users wishes to exchange information with the help of a nonregenerative multiantenna relay. A low-complexity joint beamforming and power management scheme is proposed. The proposed beamformers first align the channel matrices of the user pair and then decompose the aligned channel into parallel subchannels. Two power management issues, i.e., power allocation and power control, are addressed in this paper. First, sum-rate optimizing power allocation is proposed to allocate power between all subchannels and nodes. Second, quality of service (QoS) satisfying power control is proposed to minimize the total transmission power in the network. Simulation results justify that the proposed joint beamforming and power management scheme delivers better sum-rate performance or consumes lower transmission power when compared with existing schemes.

Feasibility study of LTE signal as a new illuminators of opportunity for passive radar applications

Recently, there has been an evolution of mobile networks towards the fourth generation radio wireless communications (4G) as LTE (Long Term Evolution). In this paper, the feasibility of using LTE-based passive radar is investigated to take advantage of using LTE signal as illuminator of opportunity for moving object monitoring. An analysis of ambiguity function is done on a typical LTE waveform to assess the Doppler and range characteristics. The initial results and analysis show that LTE signal range and Doppler resolutions of 7.5m and 0.11m/s can be achieved, respectively.

Multiobjective Beampattern Optimization in Collaborative Beamforming via NSGA-II With Selective Distance

Collaborative beamforming is usually characterized by high, asymmetrical sidelobe levels due to the randomness of node locations. Previous works have shown that the optimization methods aiming to reduce the peak sidelobe level (PSL) alone do not guarantee the overall sidelobe reduction of the beampattern, especially when the nodes are random and cannot be manipulated. Hence, this paper proposes a multiobjective amplitude and phase optimization technique with two objective functions: PSL minimization and directivity maximization, in order to improve the beampattern. A novel selective Euclidean distance approach in the nondominated sorting genetic algorithm II (NSGA-II) is proposed to steer the candidate solutions toward a better solution. Results obtained by the proposed NSGA with selective distance (NSGA-SD) are compared with the single-objective PSL optimization performed using both GA and particle swarm optimization. The proposed multiobjective NSGA provides up to 40% improvement in PSL reduction and 50% improvement in directivity maximization and up to 10% increased performance compared to the legacy NSGA-II. The analysis of the optimization method when considering mutual coupling between the nodes shows that this improvement is valid when the inter-node Euclidean separations are large.

Two-way secrecy schemes for the broadcast channel with internal eavesdroppers

The secrecy problem in a broadcast setting with one source and a number of users is considered, where the message to a given user must be kept secret from all of the other users. Multi-user diversity suggests an opportunistic approach that sends a message secretly to the user with the current best channel; however, the secrecy rate goes to zero in the limit of a large number of users. Here, channel reciprocity is exploited via a two-way secrecy scheme to provide a constant positive secrecy rate to the user with the best channel. Next, motivated by the desire to transmit to a given user (rather than opportunistically to the user with the best channel), a second scheme is developed that employs relaying from other users from whom the message is still kept secret. In this non-opportunistic case, a positive secrecy rate is again shown to be achievable in the limit of a large number of system users.

Linear precoded cooperative transmission protocol for wireless broadcast channels

One of the main challenges in the wireless broadcast channels is the co-channel interference among multiple destinations. Practical linear precoding techniques such as zero-forcing beamforming (ZFBF) is used to avoid the co-channel interference. However, the achievable diversity order of the ZFBF is bounded by the number of transmitter antennas. In this paper, we introduce a spectral efficient cooperative broadcast channels transmission protocol in the MISO channels using linear precoding. We evaluate the performance of the proposed protocol using the diversity and multiplexing tradeoff. The proposed protocol can achieve the maximum diversity order expressed as a sum of the transmitter antennas and the number of participating relays. For a large number of relay candidates, the diversity and multiplexing tradeoff of the proposed protocol completely surpasses the performance of the comparable scheme. Simulations have also shown the outage probability of the proposed protocol outperforms the existing scheme.

Performance Evaluation of Localization Accuracy for a Log-Normal Shadow Fading Wireless Sensor Network under Physical Barrier Attacks

Localization is an apparent aspect of a wireless sensor network, which is the focus of much interesting research. One of the severe conditions that needs to be taken into consideration is localizing a mobile target through a dispersed sensor network in the presence of physical barrier attacks. These attacks confuse the localization process and cause location estimation errors. Range-based methods, like the received signal strength indication (RSSI), face the major influence of this kind of attack. This paper proposes a solution based on a combination of multi-frequency multi-power localization (C-MFMPL) and step function multi-frequency multi-power localization (SF-MFMPL), including the fingerprint matching technique and lateration, to provide a robust and accurate localization technique. In addition, this paper proposes a grid coloring algorithm to detect the signal hole map in the network, which refers to the attack-prone regions, in order to carry out corrective actions. The simulation results show the enhancement and robustness of RSS localization performance in the face of log normal shadow fading effects, besides the presence of physical barrier attacks, through detecting, filtering and eliminating the effect of these attacks.

Geometrical Enhancement of Planar Loop Antennas for Inductive Near-Field Data Links

The low Q-factor requirements of High-Frequency Radio Frequency Identification (HF-RFID) interrogator antennas constrain transmission performance when they are used in data links requiring similar terminal antennas. This letter presents a geometrical approach to enhance the transmission performance of planar loop antennas without a significant change to their standalone performance as HF-RFID interrogator antennas. The method distributes the turns of a modified planar square loop antenna to enhance the coupling level in a symmetric link, while limiting the change in Q-factor from a conventional HF-RFID interrogator antenna. Results from a presented test case show that the design method enables a 5.75% increase in peak transmission coefficient, and a 28.42% fractional bandwidth increase in a symmetric link, compared to a conventional design.